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AP Biology
Why do we need a respiratory system?
O2
food
ATP
CO2
Need O2 in for aerobic cellular respiration make ATP
Need CO2 out waste product from
Krebs cycle
AP Biology
Optimizing gas exchange High surface area
maximizing rate of gas exchange CO2 & O2 move across cell membrane by
diffusion rate of diffusion proportional to surface area
Moist membranes moisture maintains cell membrane structure gases diffuse only dissolved in water
AP Biology
Gas exchange in many forms…
one-celled amphibians echinoderms
insects fish mammals
endotherm vs. ectothermsize
cilia
water vs. land ••
AP Biology
Counter current exchange system Water carrying gas flows in one direction,
blood flows in opposite direction
AP Biology
Blood & water flow in opposite directions maintains diffusion gradient over whole length
of gill capillary
maximizing O2 transfer from water to blood
water
blood
How counter current exchange worksfront back
blood
100%15%
5%90%
70% 40%
60% 30%
100%
5%
50%
50%
70%
30%
watercounter-current
concurrent
AP Biology
Gas Exchange on Land Advantages of terrestrial life
air has many advantages over water higher concentration of O2
O2 & CO2 diffuse much faster through air air is much lighter than water & therefore
much easier to pump
Disadvantages keeping large respiratory surface moist
causes high water loss Internal lungs
AP Biology
Terrestrial adaptations
air tubes branching throughout body
gas exchanged by diffusion across moist cells
Tracheae
Lungs Exchange tissue:spongy texture, moist epitheliumAir enters nostrils
Pharynx glottis larynx (vocal cords) trachea (windpipe) bronchi bronchioles air sacs (alveoli)Epithelial lining covered by cilia & thin film of mucus
AP Biology
Alveoli Gas exchange across thin epithelium of
millions of alveoli total surface area in humans ~100 m2
AP Biology
Negative pressure breathing Breathing due to changing pressures in lungs
pulling air instead of pushing it
Autonomic breathing control Medulla sets rhythm & pons moderates it
measures pH of blood & cerebrospinal fluid bathing brain
CO2 + H2O H2CO3 (carbonic acid)
if pH decreases then increase rate of breathing & excess CO2 is eliminated in exhaled air
Nerve sensors in walls of aorta & carotid arteriesin neck detect O2 & CO2 in blood
AP Biology
Diffusion of gases Concentration gradient & pressure
drives movement of gases into & out of blood at both lungs & body tissue
blood lungs
CO2
O2
CO2
O2
blood body
CO2
O2
CO2
O2
capillaries in lungs capillaries in muscle
AP Biology
Hemoglobin Why use a carrier molecule?
O2 not soluble enough in H2O for animal needs hemocyanin in insects = copper (bluish/greenish) hemoglobin in vertebrates = iron (reddish)
Reversibly binds O2
loading O2 at lungs or gills & unloading at cells
cooperativity
heme group
AP Biology
Cooperativity in Hemoglobin Binding O2
binding of O2 to 1st subunit causes shape change to other subunits conformational change
increasing attraction to O2
Releasing O2 when 1st subunit releases O2,
causes shape change to other subunits conformational change
lowers attraction to O2
AP Biology
O2 dissociation curve for hemoglobin
Bohr Shift drop in pH
lowers affinity of Hb for O2
active tissue (producing CO2) lowers blood pH& induces Hb to release more O2 PO2 (mm Hg)
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120 140
More O2 delivered to tissues
pH 7.60
pH 7.20pH 7.40
% o
xyh
emo
glo
bin
sat
ura
tio
n
Effect of pH (CO2 concentration)
AP Biology
O2 dissociation curve for hemoglobin
Bohr Shift increase in
temperature lowers affinity of Hb for O2
active muscle produces heat
PO2 (mm Hg)
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120 140
More O2 delivered to tissues
20°C
43°C37°C
% o
xyh
emo
glo
bin
sat
ura
tio
n
Effect of Temperature
AP Biology
Transporting CO2 in blood
Tissue cells
Plasma
CO2 dissolvesin plasma
CO2 combineswith Hb
CO2 + H2O H2CO3
H+ + HCO3–
HCO3–
H2CO3
CO2
Carbonicanhydrase
Cl–
Dissolved in blood plasma as bicarbonate ion
carbonic acidCO2 + H2O H2CO3
bicarbonateH2CO3 H+
+ HCO3–
carbonic anhydrase
AP Biology
Releasing CO2 from blood at lungsLower CO2
pressure at lungs allows CO2 to diffuse out of blood into lungs
Plasma
Lungs: Alveoli
CO2 dissolvedin plasma
HCO3–Cl–
CO2
H2CO3
H2CO3Hemoglobin + CO2
CO2 + H2O
HCO3 – + H+